This invention relates to an improved means of extending the life of rotary cone type drill bits.
Prior art drill bits of this type as would be used in mining blast hole drilling, having gaseous circulation fluid, or oilfield rotary drill bits have in common a transition surface normally referred to as the shirttail.
The shirttail is the area of the drill bit head section that transitions the head section to the gauge surface of the cone. Failure of this surface due to abrasion and/or fracture exposes the bearing surfaces or seal to the drill cuttings and rapid failure of the bit occurs. Prior art drill bits are characterized by the back face of the cone, i.e. the transition surface, forming a true 90 degree surface to the center-line of the drill bit bearing pin. Since the innermost surface of the shirttail is parallel to this surface of the cone it also forms a true 90 degree surface to the center-line of the bearing pin.
An object of this invention is to extend the life of rotary cone type drill bits by providing an effective means of protecting the shirttail area of the head sections such that premature exposure of the seals and or bearing surfaces is prevented.